This proposal requests support for research designed to examine the causes and consequences of questionable and erroneous beliefs. Some of the proposed studies continue earlier work on the misperception of random sequences and the biased selection and evaluation of information. However, the core of this proposal consists of research that examines how people's erroneous beliefs are bolstered by a tendency for people to have an inflated sense of the extent to which others think and act the way that they do. More specifically, this research seeks to explore a heretofore neglected mechanism that may underlie this "false consensus" effect, or the tendency for people to believe that their own beliefs, actions, and opinions are relatively common. This mechanism centers on the inherent ambiguity of most targets of belief. For example, when trying to assess the extent to which other people share one's belief in holistic health, one must first determine exactly what the term "holistic health" means. Such terms can be interpreted quite differently by different people, and it should be clear that the precise way that we construe such terms will not only determine our own reactions, but will exert a parallel influence on our estimates of the reactions of others. Because people fail to appreciate the extent to which others may "construe" the same object quite differently, their consensus estimates fail to take full account of an important source of potential divergence. A series of laboratory experiments will examine how such construal processes lead people to form exaggerated estimates of the commonness of their own beliefs, opinions, and behaviors, and how such distorted perceptions of consensus serve to bolster erroneous beliefs. Ultimately, this research should lead to a better understanding of the causes of, and cures for, distorted judgments, misguided decisions, and erroneous beliefs.